U.S. patent number 5,874,896 [Application Number 08/703,045] was granted by the patent office on 1999-02-23 for electronic anti-shoplifting system employing an rfid tag.
This patent grant is currently assigned to Palomar Technologies Corporation. Invention is credited to Peter R. Lowe, Donald G. Small, Jr..
United States Patent |
5,874,896 |
Lowe , et al. |
February 23, 1999 |
Electronic anti-shoplifting system employing an RFID tag
Abstract
An electronic anti-shoplifting system monitors articles of
merchandise in a sales outlet to deter shoplifting. The system is
provided with transponder tags connected to the articles of
merchandise. A tag exciter is positioned at an exit leading from
the sales outlet and generates an RF surveillance excitation
signal. If a customer carries an article through the exit without
removal authorization due to failure to pay for the article, the
transponder tag is activated, being powered by the RF surveillance
excitation signal as the customer passes the tag exciter. The
activated transponder tag generates an RF surveillance response
signal that triggers an alarm. If the customer has removal
authorization as the result of paying for the article, the
transponder tag is reprogrammed to modify the operational data
stored therein. The operational data typically includes data to
alter the frequency of an RF response signal generated by the
transponder tag, the frequency of an RF excitation signal to which
the transponder tag responds, and/or the type of modulation used by
the transponder tag to generate an RF response signal. Sales data,
such as the purchase price and date of purchase, is also stored in
the transponder tag. When the customer exits the sales outlet after
the transponder tag is reprogrammed, the transponder tag does not
generate the RF surveillance response signal that triggers the
alarm. However, the sales data stored in the transponder tag can be
accessed by the clerk of the sales outlet at a later date.
Inventors: |
Lowe; Peter R. (Colorado
Springs, CO), Small, Jr.; Donald G. (San Juan Capistrano,
CA) |
Assignee: |
Palomar Technologies
Corporation (Carlsbad, CA)
|
Family
ID: |
24823739 |
Appl.
No.: |
08/703,045 |
Filed: |
August 26, 1996 |
Current U.S.
Class: |
340/572.1;
340/13.26; 340/6.1 |
Current CPC
Class: |
G07G
1/0054 (20130101); G07G 3/003 (20130101); G08B
13/246 (20130101); G08B 13/2417 (20130101); G08B
13/2431 (20130101) |
Current International
Class: |
G07G
3/00 (20060101); G08B 13/24 (20060101); G07G
1/00 (20060101); G08B 013/187 () |
Field of
Search: |
;340/572,825,825.36,825.37 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"e5550 Standard R/W Identification Preliminary Information", Temic
Telefunken Semiconductors, pp. 93-106, Dec. 8, 1995. .
"e5550 Standard R/W Identification IC Preliminary Product
Features", Temic Eurosil, Oct. 13, 1994..
|
Primary Examiner: Swann; Glen
Attorney, Agent or Firm: Brown; Rodney F.
Claims
We claim:
1. A method for monitoring the removal of an article of merchandise
from a sales outlet comprising:
connecting a transponder tag to an article of merchandise in a
sales outlet;
positioning a tag exciter at an exit leading from said sales
outlet;
generating an RF surveillance excitation signal with said tag
exciter;
activating said transponder tag with said RF surveillance
excitation signal when said transponder tag passes said tag exciter
in the absence of removal authorization for said article;
generating an RF surveillance response signal with said activated
transponder tag in response to said RF surveillance excitation
signal;
triggering an alarm in response to said RF surveillance response
signal; and
reprogramming said transponder tag and storing sales data in said
transponder tag upon removal authorization for said article,
wherein said reprogrammed transponder tag does not generate said RF
surveillance response signal triggering said alarm when said
transponder tag passes said tag exciter.
2. The method recited in claim 1 wherein said reprogramming step
further comprises:
generating an RF write excitation signal including operational data
and said sales data;
activating said transponder tag with said RF write excitation
signal;
modifying operation of said transponder tag with said operational
data; and
storing said sales data in a non-volatile memory associated with
said transponder tag.
3. The method recited in claim 1 wherein said sales data includes
the purchase price of said article.
4. The method recited in claim 1 wherein said sales data includes
the purchase date of said article.
5. The method recited in claim 1 further comprising using an
exciter/reader/writer circuit to reprogram said transponder
tag.
6. The method recited in claim 1 wherein said operational data
includes data altering the frequency of said RF surveillance
response signal generated by said transponder tag.
7. The method recited in claim 1 wherein said operational data
includes data altering the frequency of said RF surveillance
excitation signal to which said transponder tag responds.
8. The method recited in claim 1 wherein said operational data
includes data altering the type of modulation used by said
transponder tag to generate said RF surveillance response
signal.
9. The method recited in claim 1 wherein said RF surveillance
response signal is substantially free of data.
10. The method recited in claim 1 wherein said RF surveillance
response signal has a frequency of at least about one quarter the
frequency of said RF surveillance excitation signal.
11. The method recited in claim 1 wherein said RF surveillance
response signal has a frequency about equal to one half the
frequency of said RF surveillance excitation signal.
12. An electronic anti-shoplifting system comprising:
a tag exciter positioned at an exit of a controlled area generating
an RF surveillance excitation signal;
an exciter/reader/writer circuit generating an RF writing
excitation signal containing operational and sales data and
generating an RF reading excitation signal;
a plurality of transponder tags, each transponder tag connected to
an article of merchandise located in the controlled area and each
said transponder tag including a memory and a controller having a
surveillance mode enabling said transponder tag to generate an RF
surveillance response signal after receiving said RF surveillance
excitation signal, a programming mode wherein said controller
stores said operational and sales data in said memory, and a
reading mode wherein said controller generates an RF reading
response signal containing said sales data, wherein said
exciter/reader/writer circuit receives said RF reading response
signal and outputs said sales data to an output device; and
an alarm for generating an alarm signal in response to said RF
surveillance response signal.
13. The electronic anti-shoplifting system recited in claim 12
wherein said sales data includes the purchase price of said
article.
14. The electronic anti-shoplifting system recited in claim 12
wherein said sales data includes the date of purchase of said
article.
15. A method for monitoring the removal of an article from a
controlled area comprising:
connecting a transponder tag to an article in a controlled
area;
positioning a tag exciter at an exit leading from said controlled
area;
generating an RF surveillance excitation signal with said tag
exciter;
activating said transponder tag with said RF surveillance
excitation signal when said transponder tag passes said tag exciter
in the absence of removal authorization for said article;
generating an RF surveillance response signal with said activated
transponder tag in response to said RF surveillance excitation
signal;
triggering an alarm in response to said RF surveillance response
signal; and
reprogramming said transponder tag and storing transaction data in
said transponder tag upon removal authorization for said article,
wherein said reprogrammed transponder tag does not generate said RF
surveillance response signal triggering said alarm when said
transponder tag passes said tag exciter.
16. The method recited in claim 15 wherein said reprogramming step
further comprises:
generating an RF write excitation signal including operational data
and said transaction data;
activating said transponder tag with said RF write excitation
signal;
modifying operation of said transponder tag with said operational
data; and
storing said transaction data in a non-volatile memory associated
with said transponder tag.
17. The method recited in claim 15 wherein said transaction data
includes the name of the person removing said article from said
controlled area.
18. The method recited in claim 15 wherein said transaction data
includes the removal date of said article from said controlled
area.
19. The method recited in claim 15 further comprising using an
exciter/reader/writer circuit to reprogram said transponder
tag.
20. The method recited in claim 15 wherein said operational data
includes data altering the frequency of said RF surveillance
response signal generated by said transponder tag.
21. The method recited in claim 15 wherein said operational data
includes data altering the frequency of said RF surveillance
excitation signal to which said transponder tag responds.
22. The method recited in claim 15 wherein said operational data
includes data altering the type of modulation used by said
transponder tag to generate said RF surveillance response
signal.
23. The method recited in claim 15 wherein said RF surveillance
response signal is substantially free of data.
24. The method recited in claim 15 wherein said RF surveillance
response signal has a frequency of at least about one quarter the
frequency of said RF surveillance excitation signal.
25. The method recited in claim 15 wherein said RF surveillance
response signal has a frequency about equal to one half the
frequency of said RF surveillance excitation signal.
26. A method for monitoring the removal of an article from a
controlled area comprising:
connecting a transponder tag to an article in a controlled
area;
positioning a tag exciter at an exit leading from said controlled
area;
generating an RF surveillance excitation signal with said tag
exciter;
activating said transponder tag with said RF surveillance
excitation signal when said transponder tag passes said tag exciter
in the absence of removal authorization for said article;
generating an RF surveillance response signal with said activated
transponder tag in response to said RF surveillance excitation
signal, wherein said RF surveillance response signal has a
frequency of at least about one quarter the frequency of said RF
surveillance excitation signal;
triggering an alarm in response to said RF surveillance response
signal; and
reprogramming said transponder tag upon removal authorization for
said article, wherein said reprogrammed transponder tag does not
generate said RF surveillance response signal triggering said alarm
when said transponder tag passes said tag exciter.
27. The method recited in claim 26 wherein said RF surveillance
response signal is substantially free of data.
28. The method recited in claim 26 wherein said RF surveillance
response signal has a frequency about equal to one half the
frequency of said RF surveillance excitation signal.
Description
TECHNICAL FIELD
The present invention relates generally to electronic surveillance
of merchandise in sales outlets.
BACKGROUND OF THE INVENTION
Shoplifting in sales outlets, and particularly in retail sales
outlets, is a significant problem adversely affecting both sellers
and consumers. It is estimated that retail sellers lose between $10
and $12 billion worth of merchandise annually due to shoplifting
and spend an additional $7 to $10 billion on anti-shoplifting
measures, including security devices and personnel to prevent
shoplifting. To offset the costs of shoplifting, retail sellers
pass these costs on to consumers in the form of higher prices on
merchandise. It is estimated that each household in the United
States pays retail sellers approximately $200 per year in increased
retail prices for merchandise due to the costs of shoplifting.
To deter shoplifting, some sales outlets employ electronic article
surveillance (EAS) systems that include transponder tags attached
to each article of merchandise in the sales outlet. EAS systems
further include one or more electronic readers positioned at exits
from the sales outlet to detect the transponder tags. When a
customer purchases an article, the transponder tag is disabled or
removed from the article and the customer passes by the reader and
out the exit of the sales outlet without sounding an alarm. When a
shoplifter attempts to remove an article from the sales outlet
without paying, the reader detects the transponder tag that has not
been disabled or removed from the article and sounds the alarm.
Sales or security personnel in the sales outlet are alerted by the
alarm, enabling them to apprehend the shoplifter and recover the
merchandise.
Although EAS systems are effective in reducing losses incurred by
sales outlets due to theft of merchandise without payment, retail
sales outlets employing EAS systems remain susceptible to other
forms of shoplifting. Many retail sellers allow customers to freely
return merchandise purchased from the sales outlet, even in the
absence of proof of purchase, if the article being returned is
carried by the sales outlet. Some customers, however, purchase
merchandise at reduced sale prices from a retail sales outlet and
return the merchandise to the same sales outlet for exchange or
refund, claiming to have paid full price for the merchandise. If
the seller refunds the full price, the seller loses the amount in
excess of the purchase price in addition to the cost of processing
the returned merchandise. Other retail sellers provide price
guarantees having time limits. If a customer purchases an article
of merchandise from a seller and subsequently discovers that the
article is sold elsewhere at a lower price or that the original
seller has dropped the price of the article after the customer's
purchase date, but before the expiration of the price guarantee
time limit, the customer is entitled to a refund from the seller of
an amount at least equal to the difference between the purchase
price and the lower price. Some customers, however, attempt to
recover a refund under the price guarantee after expiration of the
time limit. Still other customers remove merchandise from one sales
outlet without paying for the merchandise and attempt to return the
merchandise to another sales outlet that sells the same merchandise
for a cash refund.
Accordingly, it is an object of the present invention to generally
improve electronic anti-shoplifting systems. It is another object
of the present invention to provide an electronic anti-shoplifting
system that deters shoplifting and deters customers from returning
sale-priced merchandise for full price. It is another object of the
present invention to provide an electronic anti-shoplifting system
that deters shoplifting and deters customers from returning
merchandise after a time-limited price guarantee expires. It is
another object of the present invention to provide an electronic
anti-shoplifting system that deters customers from stealing
merchandise from one sales outlet and returning the merchandise for
a cash refund to another sales outlet that sells the same
merchandise. It is still another object of the present invention to
provide an electronic anti-shoplifting electronic system that is
small in size and relatively inexpensive to manufacture. These
objects and others are achieved by the present invention described
hereafter.
SUMMARY OF THE INVENTION
The present invention is a method and apparatus for monitoring the
removal of articles of merchandise from a controlled area, such as
a sales outlet, to deter shoplifting of merchandise from the sales
outlet. The apparatus includes a plurality of transponder tags and
a tag exciter. The transponder tags are connected to the articles
of merchandise on display to customers in the sales outlet. The tag
exciter is positioned at the customer exit leading from the sales
outlet and generates an RF surveillance excitation signal that is
transmitted to the transponder tag as it passes by the tag exciter
through the exit. If a customer carries an article of merchandise
through the exit without removal authorization due failure to pay
for the article, the transponder tag connected to the article is
activated, being powered by the RF surveillance excitation signal
from the tag exciter. The activated transponder tag generates an RF
surveillance response signal in response to the RF surveillance
excitation signal and the RF surveillance response signal triggers
an alarm.
If the customer obtains removal authorization by paying for the
article, the transponder tag is reprogrammed to modify the
operational data stored therein. The operational data typically
includes data to alter the frequency of the RF response signal
generated by the transponder tag, the frequency of the RF
excitation signal to which the transponder tag responds, and/or the
type of modulation used by the transponder tag to generate the RF
response signal. Sales data, such as the purchase price and date of
purchase, is also stored in the transponder tag. When the customer
exits the sales outlet after the transponder tag is reprogrammed,
the transponder tag does not generate the RF surveillance response
signal that triggers the alarm.
The present invention will be further understood, both as to its
structure and operation, from the accompanying drawings, taken in
conjunction with the accompanying description, in which similar
reference characters refer to similar parts.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an anti-shoplifting electronic system
according to the present invention in a sales outlet.
FIG. 2 is a block diagram and electrical schematic of an
exciter/reader/writer circuit, an exciter, a transponder tag and an
alarm for the anti-shoplifting electronic system of FIG. 1.
FIG. 3 is a block diagram and electrical schematic of the
exciter/reader/writer circuit for the anti-shoplifting electronic
system of FIGS. 1 and 2.
FIG. 4 is a block diagram and electrical schematic of the exciter
for the anti-shoplifting electronic system of FIGS. 1 and 2.
FIG. 5 is a block diagram and electrical schematic of the alarm for
the anti-shoplifting electronic system of FIGS. 1 and 2.
DESCRIPTION OF PREFERRED EMBODIMENTS
Radio frequency (RF) transponder systems are used to communicate
between remote locations without direct electrical contact
therebetween. RF transponder systems generally include an
exciter/reader (ER) and a transponder, otherwise termed an RF
identification (RFID) tag. The ER generates an RF excitation signal
and transmits it to the transponder that is energized thereby,
causing the transponder to generate an identification signal or
other data signal and transmit it back to the ER at a particular
frequency. RF transponder systems are commonly used to identify or
indicate the presence of an object to which the RFID tag is
connected or to transmit information relating to a physical
condition such as the air pressure of a tire or the temperature of
a fluid in a container.
Electronic article surveillance (EAS) systems include transponder
tags attached to articles of merchandise in a sales outlet. The EAS
systems also include readers positioned at the exits leading from
the sales outlet. When a customer attempts to shoplift merchandise
from the sales outlet by removing an article without paying for it,
the reader generates an excitation signal that powers the
transponder tag. The transponder tag generates a response signal
that triggers an alarm associated with the reader or a stand-alone
alarm. If a customer purchases the merchandise, the transponder tag
is disabled or removed. The present invention combines the
desirable features of both EAS systems and RF transponder systems
to provide an electronic anti-shoplifting system.
Referring now to FIG. 1, an electronic anti-shoplifting system
according to the present invention is shown. A sales outlet
generally designated 10 includes one or more exits such as a
doorway 12 through which customers depart the sales outlet 10.
The sales outlet 10 includes retail space 14 in which articles of
merchandise generally designated 20 are displayed for sale to the
customers. For example, the articles of merchandise may include
multiple personal stereo systems 30, 32, 34, and 36, miniature
portable televisions 40, 42, 44 and 46, and cameras 50, 52, and 54.
Skilled artisans can appreciate that the articles may include any
type of merchandise. Skilled artisans can further appreciate that,
in addition to sales outlets, the present electronic
anti-shoplifting device has application to substantially any
controlled area. Transponder tags 58 are physically connected by a
fastener (not shown) to the articles of merchandise 20. Preferably,
the fastener cannot be removed without a special removal tool or
key not available to the general public. Such fasteners are known
in the art and are not be described further herein.
The electronic anti-shoplifting system includes the transponder
tags 58, one or more exciter/reader/writer (ERW) circuits 60, one
or more exciters 70 and one or more alarms 75. The ERW circuit 60
is preferably located at the point of sale, such as a cash register
80. The exciter 70 is preferably located at the exit 12 leading
from the sales outlet 10 such that customers must pass by the
exciter 70 with any articles 20 in their possession before exiting
the sales outlet 10. The alarm 75 is located near the exciter 70.
The exciter 70 generates and transmits an RF surveillance
excitation signal. The transponder tag 58 receives the RF
surveillance excitation signal and, in the absence of a purchase
authorization, responds thereto by generating and transmitting an
RF surveillance response signal. The alarm 75 receives the RF
surveillance response signal. Alternately an exciter/reader can be
employed to perform both functions of generating the RF
surveillance excitation signal and receiving the RF surveillance
response signal. Skilled artisans can appreciate that the sales
outlet 10 may include additional exits 12 associated with
additional exciters 70, alarms 75, cash registers 80 and/or ERW
circuits 60.
Referring to FIG. 2, a preferred embodiment of the electronic
anti-shoplifting system is shown and generally designated 100. The
electronic anti-shoplifting system 100 includes the ERW circuit 60,
the exciter 70, the alarm 75 and the transponder tag 58. The
transponder tag 58 includes an analog front end 110 having inputs
connected to an antenna coil 116, a capacitor 118, and a modulator
120 and having outputs connected to a write decoder 124 and a
bitrate generator 128. An output of the write decoder 124 is
connected to a first input of a mode register 136. The mode
register 136 has outputs coupled to the modulator 120 and a logic
controller 138. A second input of the mode register 136 is coupled
to a first output of the memory 140. The first and second outputs
of the controller 138 are coupled to a first input of the memory
140 and an input register 144 of the memory 140, respectively. A
voltage generator 150 has an output coupled to the input register
144.
The analog front end 110 generates power from the current induced
on the antenna coil 116 by the RF reading, writing, or surveillance
excitation signal, which is a magnetic field produced by the ERW
circuit 60 or the exciter 70. The analog front end 110 controls the
bidirectional data communications with the ERW circuit 60, the
exciter 70, and the alarm 75. The analog front end 110 rectifies
the AC coil voltage to generate a DC supply voltage to power the
transponder tag 58 and extracts a clock signal from the AC coil
voltage. By way of example, the analog front end 110 selectively
switches a load across opposite nodes of the antenna coil 116 when
transmitting the response signal from the transponder tag 58 to the
ERW circuit 60 or the alarm 75 during the reading or surveillance
modes. The analog front end 110 also detects a field gap that
occurs when the ERW circuit 60 is attempting to write information
into the memory 140 during the writing mode. The controller 138
loads the mode register 136 with operational data from the memory
140 after power-on and during reading to minimize errors. The
controller 138 controls reading and writing access to the memory
140. If the password is enabled, the controller 138 compares a
password transmitted by the ERW circuit 60 to the password stored
in memory 140 to grant or deny reading or writing access to the
data stored in the memory 140.
The bitrate generator 128 allows the selection of bitrates which
are a fractional portion of the frequency of the RF excitation
signal. Typically, the bitrate generator allows selection of the
following bitrates: RF/8, RF/16, RF/32, RF/40, RF/50, RF/64,
RF/100, and RF/128, where RF equals the frequency of the RF
excitation signal. With slight modification of the bitrate
generator 128, additional bitrates of RF/2 and RF/4 are provided to
maximize signal power of the RF surveillance response signal during
the surveillance mode as described hereafter. The write decoder 124
determines whether a write data stream from the ERW circuit 60 is
valid. The voltage generator 150 generates a supply voltage for
programming the memory 140 during a write signal. The mode register
136 stores the mode data from the memory 140 and periodically
refreshes the mode data during the reading mode. The modulator 120
allows selection of various different modulation schemes for the
reading response signal including: frequency shift key (FSK); phase
shift key (PSK); Manchester; biphase; and combinations thereof. The
memory 140 is preferably EEPROM.
In operation, a customer enters the sales outlet 10. If the
customer attempts to shoplift an article of merchandise, such as
the camera 50, the exciter 70 generates an RF surveillance
excitation signal 182 that triggers the transponder tag 58. The
transponder tag 58, that is connected to the camera 50 and is in a
surveillance mode, generates an RF surveillance response signal
184. In any case, the alarm 75 receives the RF surveillance
response signal 184 and generates a visual or audible signal to
alert security personnel. Alternately, an exciter/reader receives
the RF surveillance response signal 184 from the transponder tag 58
and triggers an alarm integral with the exciter/reader that alerts
security personnel. The RF surveillance response signal 184 is
preferably transmitted free of any data when the transponder tag 58
is in the surveillance mode. The RF surveillance signal 184
activates the alarm simply by its presence and the alarm remains
inactive when the RF surveillance signal 184 is absent. The RF
surveillance signal 184 is preferably transmitted to the alarm at
as great a power level as possible to maximize the transmission
range of the RF surveillance signal 184 and correspondingly the
real range of the ERW circuit 60. A relatively high power level is
achieved by returning the RF surveillance signal 184 to the alarm
at a single frequency corresponding to a selected bitrate
preferably greater than RF/4 and more preferably a selected bitrate
of RF/2.
If the customer purchases an article of merchandise such as the
stereo 30, the customer selects the stereo 30 and brings the stereo
30 to the cash register 80. A sales clerk positions the transponder
tag 58 attached to the stereo 30 adjacent the ERW circuit 60 and
actuates a reprogramming mode that reprograms the transponder tag
58. During the reprogramming mode, the ERW circuit 60 generates an
RF write excitation signal 186 received by the transponder tag 58.
The RF write excitation signal 186 generated by the ERW circuit 60
actuates a writing circuit in the transponder tag 58 that writes
sales data and/or operational data contained in the write signal
into the non-volatile memory of the transponder tag 58.
The sales data preferably includes the time and date of sale, name
of customer and the purchase price. The sales data may also include
merchandise identification data or other descriptive information
concerning the article of merchandise. In the example above, the
sales data written into the transponder tag 58 coupled to the
stereo 30 includes the name of customer the purchase price, the
time and date of sale, the model number, the manufacturer, or other
information concerning the stereo 30. Preferably, the write circuit
of the transponder tag 58 requires a password. The ERW circuit 60
outputs the password as an initial portion of the write excitation
signal 186. The writing circuit of the transponder tag 58 will not
write the sales data into the non-volatile memory of the
transponder tag 58 before receiving the password.
During the reprogramming mode, operation of the transponder tag 58
is altered such that it is disabled relative to the exciter 70, but
not relative to the ERW circuit 60. Consequently, when the customer
exits the sales outlet 10 through one of the exits 12, the
transponder tag 58 and the exciter 70 do not trigger the alarm 75.
To that end, the write signal generated by the ERW circuit 60
includes operational data that changes the operation of the
transponder tag 58. Preferably the operational data contained in
the write signal changes the frequency of the RF response signal,
the frequency of the RF excitation signal to which the transponder
tag 58 responds, and/or the type of modulation used by the
transponder tag 58 to generate the RF response signal. After the
programming mode is completed and the transponder tag 58 is in the
data mode, the transponder tag 58 does not respond when passing
through the exciter 70. Therefore, the alarm is not erroneously
triggered.
When a customer subsequently returns a previously purchased article
of merchandise, the sales clerk actuates a reading mode of the ERW
circuit 60. The ERW circuit 60 generates a reading excitation
signal 188 received by the transponder tag 58. The transponder tag
58 is powered by the reading excitation signal 188 and generates a
reading response signal 190 including the sale data previously
stored in the non-volatile memory of the transponder tag 58. The
ERW circuit 60 receives the reading response signal 190 from the
transponder tag 58. The cash register 80 and/or the ERW circuit 60
outputs the sales data to the sales clerk.
As can be appreciated, the sales clerk reviews the sales data
before deciding whether a refund is authorized and the appropriate
amount of the refund. If the article was on sale when the customer
purchased the article, the sales clerk will know the reduced sale
price and will not refund the full price of article. If the refund
is in response to a time-limited price guarantee, the sales clerk
knows when the article was purchased and will not provide refunds
on articles where the time limit of the price guarantee has
expired. If the article lacks a transponder tag 58, the sales clerk
can reasonably conclude that the article was not purchased from the
sales outlet 10 and void a refund.
In a preferred embodiment, the transponder tag 58 includes a Temic
e5550 Read/Write Identification Integrated Circuit (IDIC.RTM.)
available from Temic Eurosil, Eching, Germany. Details of the Temic
e5550 IDIC.RTM. are provided in "e5550 Standard R/W Identification
IC Preliminary Product Features" dated Oct. 13, 1994 and in "e5550
Standard R/W Identification IC Preliminary Information" dated Dec.
12, 1995, both of which are incorporated herein by reference.
A suitable ERW circuit is a conventional reader modified to
modulate its excitation in accordance with the method described in
the above-cited references that can be mechanically configured for
mounting in various types of environments. Referring to FIG. 3, the
ERW circuit is shown and generally designated 60. The ERW circuit
60 has three main functional units: an exciter/writer 200, a signal
conditioner circuit 202, and a demodulation and detection circuit
204.
The exciter/writer circuit 200 consists of an AC signal source 216
followed by a power amplifier 218 that amplifies the signal
generated by the AC signal source to provide a high current, high
voltage reading or writing excitation signal to a capacitor 220 and
an antenna coil 222. The inductance of the antenna coil 222 and the
capacitance of the capacitor 220 are selected to resonate at the
excitation signal frequency so that the voltage across the antenna
coil 222 is greater than the voltage output of the power amplifier
218. The AC signal source 216 provides the reading or writing
excitation signal that can include an identification code for the
transponder Tag 58 and/or write data to be written into the memory
44 of the transponder tag 58.
The signal conditioner circuit 202 is also coupled to the antenna
coil 222 and serves to amplify the RF reading response signal
generated by the transponder tag 58. The signal conditioner circuit
202 filters out the RF reading excitation signal frequencies as
well as other noise and undesired signals outside of the frequency
range of the transponder tag signals. The signal conditioner
circuit 202 includes a first filter 224 that passes the RF reading
response signal frequency returned from the transponder tag 58. A
first amplifier 228 increases the signal strength of the signal
output by the first filter 224. A second filter 232 passively
excludes the high energy at the excitation frequency. A second
amplifier 234 increases the signal strength of the signal output by
the second filter 232. Preferably the filters 224 and 232 include
abandpass filter and a bandstop filter. Skilled artisans can
appreciate that the relative positions of the first and second
filters can be switched or a higher order filter providing both
bandpass and bandstop filtering functions can be employed. The
first and second amplifiers 228 and 234 can also be combined into a
single amplifier.
The amplified output of the signal conditioner circuit 202 is input
to a filter 250 of the demodulation and detection circuit 204 that
further reduces the excitation signal energy. Preferably the filter
250 is a low pass filter. The demodulation and detection circuit
204 also includes a demodulation circuit 254 and a microcomputer
generally designated 256. The microcomputer 256 includes an
input/output interface 258, a memory 262, and a microprocessor or
control logic 266. The demodulation circuit 254 is typically a FSK
demodulator that includes a phase-locked loop circuit configured as
a tone detector. The demodulation circuit 254 and the microcomputer
256 extract data from the response signal. To extract the data,
digital signals are generated when the return signal from the
transponder tag 58 shifts between two frequencies. The timing of
the transitions of the digital signals between the logic levels or
frequencies is detected. The information obtained by the
microcomputer 256 can be stored in the memory 262 or transferred to
an output device 270 such as a display, a printer, a network,
another computer or other devices or storage media.
Referring to FIG. 4, the exciter 70, which is a simplified form of
the ERW circuit 60, is illustrated. The exciter 70 includes a
signal source 280 that generates an RF surveillance excitation
signal, the power amplifier 218, the capacitor 220 and the antenna
222. Referring to FIG. 5, the alarm 75 includes an inductive coil
282, a bandpass filter 284 and a power amplifier 288 that pass and
amplify the RF surveillance response signal generated by the
transponder tag 58. A threshold detector 290 generates an alarm
trigger signal to an output device 294 if the surveillance response
signal exceeds the preset threshold of the threshold detector 290.
The output device 294 is preferably a visual or audible alarm. The
exciter 70 and the alarm 75 can be combined into a signal
exciter/reader or alarm circuit.
Applicant has illustrated the method according to the present
invention with the exemplary electronic anti-shoplifting system
described above. Skilled artisans will realize that other circuits
can be substituted for the transponder tag 58, ERW circuit 60,
exciter 70, and alarm 75 described above without departing from the
teachings of the present invention. For example, instead of using
contactless reprogramming of the transponder tag 58 described
above, programming through direct contact can be used as taught in
U.S. Pat. No. 4,730,188 to Milheiser which is incorporated herein
by reference. Contactless programming can be performed using other
methods. For example, several different methods of contactless
programming an RF transponder are known including "Coded
Information Arrangement", U.S. Pat. No. 4,399,437 to Falck et al.
and commonly assigned patent applications entitled "Contactless
Programmable Radio Frequency Transponder", U.S. Ser. No.
08/540,631, filed Oct. 11, 1995, "RF Identification Tag and
Contactless Method of Programming the Same", U.S. Ser. No.
08/514,712, filed Aug. 14, 1995, and "High Field Programmable
Transponder System and Method", U.S. Ser. No. 08/316,653, filed
Sep. 30, 1994, now abandoned all of which are incorporated herein
by reference. Still other methods of contactless programming will
be apparent to skilled artisans.
While the foregoing preferred embodiments of the invention have
been described and shown, it is understood that alternatives and
modifications, such as those suggested and others, may be made
thereto and fall within the scope of the invention.
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